Polish the keybinding implementation a bit.

chrome/common/extensions/extension_constants.h

Index: chrome/common/extensions/extension_constants.h
===================================================================
--- chrome/common/extensions/extension_constants.h	(revision 127690)
+++ chrome/common/extensions/extension_constants.h	(working copy)
@@ -100,6 +100,7 @@
   extern const char kShiftKey[];
   extern const char kShortcutKey[];
   extern const char kSignature[];
+  extern const char kSuggestedKey[];
   extern const char kTheme[];
   extern const char kThemeColors[];
   extern const char kThemeDisplayProperties[];
@@ -134,6 +135,10 @@
   extern const char kIntentDispositionWindow[];
   extern const char kIntentDispositionInline[];
   extern const char kIsolatedStorage[];
+  extern const char kKeybindingPlatformChromeOs[];
+  extern const char kKeybindingPlatformLinux[];
+  extern const char kKeybindingPlatformMac[];
+  extern const char kKeybindingPlatformWin[];
   extern const char kLaunchContainerPanel[];
   extern const char kLaunchContainerShell[];
   extern const char kLaunchContainerTab[];
@@ -220,6 +225,7 @@
   extern const char kInvalidJsList[];
   extern const char kInvalidKey[];
   extern const char kInvalidKeyBinding[];
+  extern const char kInvalidKeyBindingMissingPlatform[];
   extern const char kInvalidKeyBindingDescription[];
   extern const char kInvalidKeyBindingDictionary[];
   extern const char kInvalidLaunchContainer[];